Equilibrium partition of rapeseed oil between supercritical CO2 and prepressed rapeseed

Abstract

The equilibrium partition of a vegetable extract between supercritical (SC) CO2 (fluid phase) and a vegetable substrate (solid phase) is commonly best-fitted in the mathematical simulation of extraction curves. The aim of this study was to develop and apply an experimental methodology to measure the equilibrium partition of rapeseed oil between SC CO2 and prepressed rapeseed. We measured and modelled sorption isotherm/isobar curves using a methodology that intersperses extraction (to reduce oil content) and equilibration (by recirculation of the SC CO2 phase) steps, with oil being sampled in each step. Oil desorption was a two-stage process; when rapeseed contains more than similar to 70-80 g kg(-1) oil/substrate the SC CO2 phase gets saturated with oil (C-f = C-sat), whereas when it contains less oil this is bound to the solid matrix in such a way that C-f dips below C-sat. Increasing pressure from 22 to 28 MPa at constant temperature (40 degrees C) increases C-f. The effect of the increase in pressure is less pronounced when SC CO2 density is kept constant (857.1 kg/m(3)) by simultaneously increasing temperature from 40 to 50 degrees C. The heat of desorption of the oil is similar to 100 kJ/mol which suggests it is bound to the prepressed seed by van der Waals interaction forces. However experimental values in this region are uncertain due to propagation of uncertainties to estimate C-s.